In DE 102009041735, such a seal is disclosed, comprising:                a seal body integrating a chamber:                    a wall of which projects into a space,            and in which a switching-over element that switches over by deforming the chamber is disposed,                        and a lever for actuating the switching-over element, the lever tilting with respect to the body, including the chamber, in two different directions, and comprising:                    on a side facing said space, a surface suitable for acting on the wall of the chamber during tilting, and            on an opposite side, a protuberance which, under the action of an external activation element, rocks the lever.                        
The switching-over element (or member sensitive to pressure) may, for example, be an electrical sensitive strip, an optical fibre, a column of air, etc.
Typically, the objective is then to have a seal, in particular for a train, metro, tram, etc. equipped with a sensitive element or switching-over element, which fulfils the anti-drag function.
The anti-drag function makes it possible in particular to prevent persons situated on a platform where the rail vehicle is passing and wedged by the closure of the doors (via a garment, a bag strap, etc.) being pulled by the vehicle. This type of dragging may in fact injure or even cause the death of the person. An object (or what can be termed generically “an external actuation element”) capable of acting on the lever in order to switch over the switching-over element and which is wedged in the seal, typically with the door closed, outside, may also be dragged by the moving vehicle, from the inside of the vehicle.
One problem is that these safety measures degrade the availability of the vehicles in question, because of the frequent re-opening of the doors (after normal closures), departures of delayed trains, etc.